Many people suffer from eye conditions and diseases that can be corrected or treated with lenses that vault the cornea and rest on the sclera (referred to herein as “scleral lenses”). These lenses are distinguished from the more common corneal contact lenses which rest on the cornea. For reference, an illustration depicting a scleral lens vaulting over an irregular cornea and resting on the sclera is shown in FIG. 1. As shown in FIG. 1, sclera 105 refers to the dense, white, fibrous outer layer of the eyeball that is continuous with the cornea 112 at the front of the eye. A scleral lens 120 rests on the sclera 105 and vaults the cornea 112 with a reservoir 115 that is filled with artificial tears at the time of application. Modern scleral lenses are made of gas-permeable plastic that allows for transmission of atmospheric oxygen, and are characterized by a shape that allows for retention of fluid in the reservoir and tear exchange, 115 so as to meet the underlying cornea's physiologic needs.
FIG. 2 shows certain scleral lens parameters that characterize the design of a scleral lens. The sagittal height 210 refers to the perpendicular distance between the diameter at the 12 mm chord 245 and the apex 225. The haptic angle 220 refers to an angle between a straight (reference) tangent line 230 and a diameter of the scleral lens. This angle can characterize the relationship between the haptic portion and transitional zone 235 of the scleral lens. The haptic zone 240 refers to the portion of the lens that rests on the sclera.
Corneal contact lenses can be fitted using an “empiric” approach, in which measurements of the contour of the cornea are obtained, and on that basis a lens is selected or designed for the eye. The instruments used to measure the eye do not have the range to take measurements for the larger scleral diameter. Furthermore, these instruments depend on transparency or reflection, neither of which is characteristic of the scleral portion of the eye. Typically, scleral lenses are fitted to the individual eye in a “diagnostic” approach, in which a trial lens is placed on the eye and fit is assessed. This process is iterative with subsequent trial lenses selected, modified, or designed to address deficiencies of the prior trial lens. Typically, multiples trial lenses and wearing trials are required. Ill-fitting lenses may not meet the visual needs of the patient and can compromise the health of the eye. Some eyes cannot be fitted because of the unique contour and/or constraints intrinsic to the design and manufacture of scleral lenses. However, this may not be apparent until many scleral lens fitting and wearing trials are undertaken for that eye.